1. Field of the Invention
This invention relates to a wide range radiation detector for detecting radiations in wide range energy regions, and more particularly relates to a radiation detector for detecting radiations in high energy regions highly sensitively.
2. Description of the Prior Art
FIG. 21 is a block diagram showing a construction of a conventional wide range radiation detector. In the figure, reference numeral 1 designates a semiconductor element. Reference numerals 2, 3 and 4 designate radiations incident on the semiconductor element 1. Reference numeral 5 designates a preamplifier for taking out and amplifying output pulses having pulse heights proportional to the energy of radiations absorbed in the semiconductor element 1. Reference numeral 6 designates a main amplifier connected to the preamplifier 5. Reference numeral 7 designates an analog-digital converter connected to the main amplifier 6. Reference numeral 8 designates a multi-channel pulse height analyzer connected to the analog-digital converter 7.
Next, the operation of the wide range radiation detector structured as above will be described. At first, the radiations 2, 3 and 4 enter the semiconductor element 1. Then, the whole energy of the radiation 2 is absorbed in the semiconductor element 1; the radiation 3 passes through the semiconductor element 1 without any interaction; the radiation 4 causes, for example, Compton scattering in the semiconductor element 1, so that the energy of the radiation 4a is absorbed and the energy of the radiation 4b is emitted to the outside of the element 1 without being absorbed.
Consequently, only the output pulses having pulse heights proportional to the energy of the radiations 2 and 4a are outputted from the semiconductor element 1. Then, the output pulses are amplified by the preamplifier 5 and the main amplifier 6 to be converted from analog signals to digital signals by the analog-digital converter 7. And further, the converted digital signals are counted by the multi-channel pulse height analyzer 8 by every pulse height value. Thus, the energy distributions and the dose rates of the radiations incident on the semiconductor element 1 are measured on the basis of the results of the analysis of the multi-channel pulse height analyzer 8.
Since the conventional wide range radiation detector is structured as above, high energy region radiations cannot be detected accurately because they pass through without any interaction like the radiation 3 or cause Compton scattering and so forth like the radiation 4 so that the whole energy of them are not absorbed but a part of the energy of them is emitted to the outside of the semiconductor element 1. Accordingly, the followings can be considered for resolving the above problem. At first, it is considerable to cope with high energy region radiations by increasing the thickness of the semiconductor element 1 itself. But it is very difficult to form the thickness of the semiconductor element 1 up to an extent capable of coping with the high energy region radiations by means of traditional semiconductor manufacturing skills. Alternately, it is also possible to cope with the high energy region radiations by increasing the area of the semiconductor element 1 itself and disposing the longer side of the element 1 in parallel with the incident directions of the radiations. But the plan can not be adopted in spite of the capability for detecting the high energy region radiations, because the part of the semiconductor element 1 for detecting radiations would be very narrow owing to the thin thickness direction of the element 1 to be disposed parallel to the incident thereof. Another problem of the plan is that the whole energy given to the element by radiations cannot be transmitted to outer circuits in the case of semiconductors whose mobility of charge carriers is small. The reason is that the collection of charges becomes insufficient because some generated charges cannot reach collection electrodes owing to the small mobility of charge carriers.